EXPERIMENTS IN CHEMISTRY 29 



discovery. He was received in Biot's laboratory. 

 The old scientist insisted on furnishing his own 

 materials for the demonstration, and Pasteur made 

 the required solutions in his presence. In the words 

 of Pasteur who has left us a description of this 

 interview, "The solution was then placed in his 

 laboratory and allowed slowly to evaporate; when 

 thirty to forty grams of the crystals had separated, 

 he again called me to the College de France to col- 

 lect and distinguish by their crystallographic char- 

 acter the right and the left rotating crystals from 

 one another, under his direct observation; he bade 

 me repeat the declaration that the crystals which 

 I had placed in his right hand would rotate the 

 plane of polarization to the right, and the others 

 would rotate it to the left. 



"After this had been done, he declared that he 

 himself would complete the experiments. He pre- 

 pared the carefully weighed solutions and, when he 

 was ready to make the observations in the polariz- 

 ing apparatus, he called me again into his labora- 

 tory. He put first into the apparatus the most in- 

 teresting solution, the one which should rotate 

 toward the left. Without making a reading, but 

 upon the instant, he noted a change in color in the 

 two halves of the field of vision, and he recognized 



